Temperature responsive devices, and particularly valves, are frequently used in the area of fire detection and control. For example, thermally responsive valves are used in sprinkler systems to put out fires. A difficulty with these types of valves however is that after putting out the fire the damage caused by a continuing flow of water can be substantial. Since statistics show that greater than 80% of fires occur during idle hours, a sprinkler system could put out a small fire and continue to run for a substantial period of time before discovered. Thus, while sprinklers do less damage than fires and fire hoses, they still cause large losses and unnecessary dollar loss because they do not turn themselves off. Further, if the sprinklers were accidentally discharged they would continue to run until someone turned them off. In use a standard sprinkler system will deliver only about one eighth of the amount of water per minute that a fire hose will, but nevertheless, the water damage over even a short period of time can still be substantial. It would be advantageous if some method were provided for the sprinkler system to turn off after extinguishing a fire.
There are a variety of methods available for providing thermally responsive devices for use in fire-sensing and sprinkler applications. Some of the techniques are used in combined sensor/actuator sevices such as a frangible glass bulb or a fusable link sprinkler, while others are sensor-only such as electronic temperature sensors or smoke detectors. Actuator only devices could be solenoid or pyrotechnic actuated valves. The most common technique used for sprinklers is the fusable link. These links contain metal alloys which melt rapidly at a predetermined temperature. The fusable link is used to secure a spring linkage under tension. When the alloy melts, the spring action is released, opening a water passage.
The frangible glass bulb technique is comprised of a high vapor pressure liquid and a small air bubble used as a strut to maintain a normally open water passage. When exposed to heat, the liquid expands, compressing the air bubble. When the bubble is completely absorbed, there is a rapid increase in pressure shattering the bulb and allowing water flow. The desired temperature rating is obtained by controlling the size of the air bubble relative to the amount of liquid in the bulb. Glass bulb sprinklers are widely used, relatively inexpensive, and reliable, but also do not have the capability to turn off after use.
In the category of sensing devices there are electronic temperature sensors, electronic gas sensors, and photoelectric and gas ironizations smoke detectors. Electronic sensors are thermistors, thermal resistors and transistors, which are temperature sensitive and can drive analog outputs. Electronic gas sensors require a power supply and are inexpensive, but they are prone to activation by non-hostile sources such as alcohol, after shave, or perfume. One such device is a metal oxide semiconductor responsive to a state of oxidation which can sense carbon monoxides and hydrocarbon levels or a lack of oxygen.
The photoelectric and gas ionization devices are utilized mainly in smoke detectors and also require a power supply. These devices are widely used as residential fire alarms. The photoelectric principle for these devices gives a somewhat faster response to products generated by fires of low energy (smouldering) as these fires generally produce large quantities of visible (larger particle) smoke. The smoke is detected by the photoelectric cell which then sets off the alarm. Other detectors using the ionization principle provide a faster response to fires of high energy (open flame) as these particles produce smaller smoke particles which are more easily detected. The techniques used in these detectors are not suitable for sprinklers as they cannot discriminate between the hostile or non-hostile smoke and may cause spurious activation. Further, if the sensitivity is decreased to small fires, a longer response time to all fires results. Numerous other techniques are available to provide temperature response, but they suffer from one or more of the same disadvantages.
The particular material used for a temperature responsive device should have high reliability, be cost effective, have an on/off capability and have no external requirements for electrical power or auxiliary equipment. Most of the materials and devices presently available described above suffer from a lack of one or more of these requirements. For example, ultraviolet and infrared flame detection devices sense either ultraviolet (UV) or infrared (IR) radiation given off by flames or glowing embers. Thus, these devices are line of sight devices and must be able to see the fire. They are subject to being blocked off by objects placed in front of them. Further, they are generally complex and beyond a typical user's budget in addition to requiring a power supply. Bimetallic devices such as those used in thermostats, would be suitable except that they again would require some type of electrical or mechanical drive system for opening and closing a valve. Detectors such as these using bimetallic or Nitinol comprised of a particular metallic sensing device have the desirable feature of automatic mechanical reset. However, they lack rapid positive action and are susceptable to false alarms from vibration of jarring.
Therefore it is a desirable object of the present invention to provide a thermally responsive valve which will shut off after extinguishing a fire. It is another object of the present invention to provide a thermally responsive valve utilizing magnetic elements which are highly reliable in sensing temperature variations.
Another object of the present invention is to provide a relatively low cost thermally responsive valve having magnetic elements.
Still another object of the present invention is to provide a thermally responsive valve in which the magnetic elements provide an on/off capability.
Still another object of the present invention is to provide a thermally responsive valve which does not need any electrical power or auxiliary equipment.
Yet another object of the present invention is to provide a magnetically activated thermally responsive valve suitable for use in sprinkler systems.